The histological microstructure and in vitro mechanical properties of the human female postmenopausal perineal body

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

OBJECTIVE

The objective of this review was to identify quantitative biomechanical measurements of human tissues, the methods for obtaining these measurements, and the primary motivations for conducting biomechanical research.

INTRODUCTION

Medical skills trainers are a safe and useful tool for clinicians to use when learning or practicing medical procedures. The haptic fidelity of these devices is often poor, which may be because the synthetic materials chosen for these devices do not have the same mechanical properties as human tissues. This review investigates a heterogeneous body of literature to identify which biomechanical properties are available for human tissues, the methods for obtaining these values, and the primary motivations behind conducting biomechanical tests.

INCLUSION CRITERIA

Studies containing quantitative measurements of the biomechanical properties of human tissues were included. Studies that primarily focused on dynamic and fluid mechanical properties were excluded. Additionally, studies only containing animal, in silico , or synthetic materials were excluded from this review.

METHODS

This scoping review followed the JBI methodology for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sources of evidence were extracted from CINAHL (EBSCO), IEEE Xplore, MEDLINE (PubMed), Scopus, and engineering conference proceedings. The search was limited to the English language. Two independent reviewers screened titles and abstracts as well as full-text reviews. Any conflicts that arose during screening and full-text review were mediated by a third reviewer. Data extraction was conducted by 2 independent reviewers and discrepancies were mediated through discussion. The results are presented in tabular, figure, and narrative formats.

RESULTS

Data were extracted from a total of 186 full-text publications. All of the studies, except for 1, were experimental. Included studies came from 33 countries, with the majority coming from the United States. Ex vivo methods were the predominant approach for extracting human tissue samples, and the most commonly studied tissue type was musculoskeletal. In this study, nearly 200 unique biomechanical values were reported, and the most commonly reported value was Young's (elastic) modulus. The most common type of mechanical test performed was tensile testing, and the most common reason for testing human tissues was to characterize biomechanical properties. Although the number of published studies on biomechanical properties of human tissues has increased over the past 20 years, there are many gaps in the literature. Of the 186 included studies, only 7 used human tissues for the design or validation of medical skills training devices. Furthermore, in studies where biomechanical values for human tissues have been obtained, a lack of standardization in engineering assumptions, methodologies, and tissue preparation may implicate the usefulness of these values.

CONCLUSIONS

This review is the first of its kind to give a broad overview of the biomechanics of human tissues in the published literature. With respect to high-fidelity haptics, there is a large gap in the published literature. Even in instances where biomechanical values are available, comparing or using these values is difficult. This is likely due to the lack of standardization in engineering assumptions, testing methodology, and reporting of the results. It is recommended that journals and experts in engineering fields conduct further research to investigate the feasibility of implementing reporting standards.

REVIEW REGISTRATION

Open Science Framework https://osf.io/fgb34.

Biaxial Murine Vaginal Remodeling With Reproductive Aging

Higher reproductive age is associated with an increased risk of gestational diabetes, pre-eclampsia, and severe vaginal tearing during delivery. Further, menopause is associated with vaginal stiffening. However, the mechanical properties of the vagina during reproductive aging before the onset of menopause are unknown. Therefore, the first objective of this study was to quantify the biaxial mechanical properties of the nulliparous murine vagina with reproductive aging. Menopause is further associated with a decrease in elastic fiber content, which may contribute to vaginal stiffening. Hence, our second objective was to determine the effect of elastic fiber disruption on the biaxial vaginal mechanical properties. To accomplish this, vaginal samples from CD-1 mice aged 2-14 months underwent extension-inflation testing protocols (n = 64 total; n = 16/age group). Then, half of the samples were randomly allocated to undergo elastic fiber fragmentation via elastase digestion (n = 32 total; 8/age group) to evaluate the role of elastic fibers. The material stiffness increased with reproductive age in both the circumferential and axial directions within the control and elastase-treated vaginas. The vagina demonstrated anisotropic mechanical behavior, and anisotropy increased with age. In summary, vaginal remodeling with reproductive age included increased direction-dependent material stiffness, which further increased following elastic fiber disruption. Further work is needed to quantify vaginal remodeling during pregnancy and postpartum with reproductive aging to better understand how age-related vaginal remodeling may contribute to an increased risk of vaginal tearing.

Decellularization of Porcine Carotid Arteries: From the Vessel to the High-Quality Scaffold in Five Hours

The use of biologically derived vessels as small-diameter vascular grafts in vascular diseases is currently intensely studied. Vessel decellularization provides a biocompatible scaffold with very low immunogenicity that avoids immunosuppression after transplantation. Good scaffold preservation is important as it facilitates successful cell repopulation. In addition, mechanical characteristics have to be carefully evaluated when the graft is intended to be used as an artery due to the high pressures the vessel is subjected to. Here, we present a new and fast decellularization protocol for porcine carotid arteries, followed by investigation of the quality of obtained vessel scaffolds in terms of maintenance of important extracellular matrix components, mechanical resistance, and compatibility with human endothelial cells. Our results evidence that our decellularization protocol minimally alters both the presence of scaffold proteins and their mechanical behavior and human endothelial cells could adhere to the scaffold in vitro. We conclude that if a suitable protocol is used, a high-quality decellularized arterial scaffold of non-human origin can be promptly obtained, having a great potential to be recellularized and used as an arterial graft in transplantation medicine.

Using virtual microscopy for the development of sampling strategies in quantitative histology and design-based stereology

Only a fraction of specimens under study are usually selected for quantification in histology. Multilevel sampling or tissue probes, slides and fields of view (FOVs) in the regions of interest (ROIs) are required. In general, all parts of the organs under study should be given the same probability to be taken into account; that is, the sampling should be unbiased on all levels. The objective of our study was to provide an overview of the use of virtual microscopy in the context of developing sampling strategies of FOVs for stereological quantification. We elaborated this idea on 18 examples from multiple fields of histology, including quantification of extracellular matrix and muscle tissue, quantification of organ and tumour microvessels and tumour-infiltrating lymphocytes, assessing osseointegration of bone implants, healing of intestine anastomoses and osteochondral defects, counting brain neurons, counting nuclei in vitro cell cultures and others. We provided practical implications for the most common situations, such as exhaustive sampling of ROIs, sampling ROIs of different sizes, sampling the same ROIs for multiple histological methods, sampling more ROIs with variable intensities or using various objectives, multistage sampling and virtual sampling. Recommendations were provided for pilot studies on systematic uniform random sampling of FOVs as a part of optimizing the efficiency of histological quantification to prevent over- or undersampling. We critically discussed the pros and cons of using virtual sections for sampling FOVs from whole scanned sections. Our review demonstrated that whole slide scans of histological sections facilitate the design of sampling strategies for quantitative histology.

The Female Pelvic Floor Fascia Anatomy: A Systematic Search and Review

The female pelvis is a complex anatomical region comprising the pelvic organs, muscles, neurovascular supplies, and fasciae. The anatomy of the pelvic floor and its fascial components are currently poorly described and misunderstood. This systematic search and review aimed to explore and summarize the current state of knowledge on the fascial anatomy of the pelvic floor in women. Methods: A systematic search was performed using Medline and Scopus databases. A synthesis of the findings with a critical appraisal was subsequently carried out. The risk of bias was assessed with the Anatomical Quality Assurance Tool. Results: A total of 39 articles, involving 1192 women, were included in the review. Although the perineal membrane, tendinous arch of pelvic fascia, pubourethral ligaments, rectovaginal fascia, and perineal body were the most frequently described structures, uncertainties were identified in micro- and macro-anatomy. The risk of bias was scored as low in 16 studies (41%), unclear in 3 studies (8%), and high in 20 studies (51%). Conclusions: This review provides the best available evidence on the female anatomy of the pelvic floor fasciae. Future studies should be conducted to clarify the discrepancies highlighted and accurately describe the pelvic floor fasciae.

Finite element modeling of maximum stress in pelvic floor structures during the head expulsion (FINESSE) study

INTRODUCTION AND HYPOTHESIS

Several studies have assessed birth-related deformations of the levator ani muscle (LAM) and perineum on models that depicted these elements in isolation. The main aim of this study was to develop a complex female pelvic floor computational model using the finite element method to evaluate points and timing of maximum stress at the LAM and perineum in relation to the birth process.

METHODS

A three-dimensional computational model of the female pelvic floor was created and used to simulate vaginal birth based on data from previously described real-life MRI scans. We developed three models: model A (LAM without perineum); model B (perineum without LAM); model C (a combined model with both structures).

RESULTS

The maximum stress in the LAM was achieved when the vertex was 9 cm below the ischial spines and measured 37.3 MPa in model A and 88.7 MPa in model C. The maximum stress in the perineum occurred at the time of distension by the suboocipito-frontal diameter and reached 86.7 MPa and 119.6 MPa in models B and C, respectively, while the stress in the posterior fourchette caused by the suboccipito-bregmatic diameter measured 36.9 MPa for model B and 39.8 MPa for model C.

CONCLUSIONS

Including perineal structures in a computational birth model simulation affects the level of stress at the LAM. The maximum stress at the LAM and perineum seems to occur when the head is lower than previously anticipated.

Urethral support in female urinary continence part 2: a computational, biomechanical analysis of Valsalva

INTRODUCTION AND HYPOTHESIS

In Part 1, we observed urethral mechanics during Valsalva that oppose current continence theories. In this study, we utilize a finite element model to elucidate the role of supportive tissues on the urethra during Valsalva. By determining the sensitivity of urethral motion and deformations to variations in tissue stiffnesses, we formulate new hypotheses regarding mechanisms of urethral passive closure.

METHODS

Anatomy was segmented from a nulliparous, continent woman at rest. The model was tuned such that urethral motion during Valsalva matched that observed in that patient. Urethra and surrounding tissue material properties were varied using Latin hypercube sampling to perform a sensitivity analysis. As in Part 1, urethral length, proximal and distal swinging, and shape parameters were measured at peak Valsalva for 50 simulations, and partial rank correlation coefficients were calculated between all model inputs and outputs. Cumulative influence factors determined which tissue properties were meaningfully influential (≥ 0.5).

RESULTS

The material properties of the urethra, perineal membrane, bladder, and paraurethral connective tissues meaningfully influenced urethral motion, deformation, and shape. Reduction of the urethral stiffness and/or the perineal membrane soft constraint resulted in simulated urethral motions and shapes associated with stress urinary incontinence in Part 1.

CONCLUSIONS

The data from Parts 1 and 2 suggest that connective tissues guide the controlled swinging motion and deformation of the urethra needed for passive closure during Valsalva. The swinging and kinking quantified in Part 1 and simulated in Part 2 are inconsistent with current continence theories.

Feasibility and safety of antepartum tactile imaging

Introduction and hypothesis

Quantitative characterization of the birth canal and critical structures before delivery may provide risk assessment for maternal birth injury. The objective of this study was to explore imaging capability of an antepartum tactile imaging (ATI) probe.

Methods

Twenty randomly selected women older than 21 years with completed 35th week of pregnancy and a premise of vaginal delivery were enrolled in the feasibility study. The biomechanical data were acquired using the ATI probe with a double-curved surface, shaped according to the fetal skull and equipped with 168 tactile sensors and an electromagnetic motion tracking sensor. Software package COMSOL Multiphysics was used for finite element modeling. Subjects were asked for assessment of pain and comfort levels experienced during the ATI examination.

Results

All 20 nulliparous women were successfully examined with the ATI. Mean age was 27.8 ± 4.1 years, BMI 30.7 ± 5.8, and week of pregnancy 38.8 ± 1.4. Biomechanical mapping with the ATI allowed real-time observation of the probe location, applied load to the vaginal walls, and a 3D tactile image composition. The nonlinear finite element model describing the stress–strain relationship of the pelvic tissue was developed and used for calculation of Young’s modulus (E). Average perineal elastic modulus was 11.1 ± 4.3 kPa, levator ani 4.8 ± 2.4 kPa, and symphysis–perineum distance was 30.1 ± 6.9 mm. The pain assessment level for the ATI examination was 2.1 ± 0.8 (scale 1–4); the comfort level was 2.05 ± 0.69 (scale 1–3).

Conclusions

The antepartum examination with the ATI probe allowed measurement of the tissue elasticity and anatomical distances. The pain level was low and the comfort level was comparable with manual palpation.

The histological microstructure and in vitro mechanical properties of pregnant and postmenopausal ewe perineal body

OBJECTIVE

The mechanical properties and microstructure of the perineal body are important for the improvement of numerical models of pelvic organs. We determined the mechanical parameters and volume fractions of the ewe perineal body as an animal model.

METHODS

The 39 specimens of 13 pregnant swifter ewes delivering by cesarean section (aged 2 years, weight 61.2 ± 6.2 kg (mean ± standard deviation) and 24 specimens of 8 postmenopausal swifter ewes 150 days after surgical ovariectomy (aged 7 years, 58.6 ± 4.6 kg)) were loaded uniaxially to determine Young's moduli of elasticity in the small (E0) and large (E1) deformation regions, and ultimate stresses and strains. The 63 adjacent tissue samples were processed histologically to assess volume fractions of smooth and skeletal muscle, adipose cells, elastin, and type I collagen using a stereological point testing grid. We compared the structural and mechanical differences along the ewe perineal body, and between pregnant and postmenopausal groups.

RESULTS

The pregnant/postmenopausal perineal body was composed of smooth muscle (12/14%; median), skeletal muscle (12/16%), collagen (10/23%), elastin (8/7%), and adipose cells (6/6%). The E0 was 37/11 kPa (median), E1 was 0.97/1.04 MPa, ultimate stress was 0.55/0.59 MPa, and ultimate strain was 0.90/0.87 for pregnant/postmenopausal perineal body. The perineal body showed a structural and mechanical stability across the sites. The pregnant ewes had a higher amount of skeletal muscle, higher E0, and a less amount of collagen when compared with postmenopausal ewes.

CONCLUSIONS

The data can be used as input for models simulating vaginal delivery, pelvic floor prolapsed, or dysfunction.